EBP (3-beta-hydroxysteroid-Delta(8),Delta(7)-isomerase; sterol Delta8-Delta7 isomerase; EC 5.3.3.5), historically identified as the emopamil-binding protein, is a multi-pass integral membrane enzyme of the endoplasmic reticulum that catalyses a post-lanosterol step of cholesterol biosynthesis. It isomerises the Delta(8) double bond of sterol intermediates to the Delta(7) position, converting zymostenol to lathosterol (in the modified Kandutsch-Russell pathway) and zymosterol to cholesta-7,24-dien-3beta-ol (in the Bloch pathway). The protein localises predominantly to the endoplasmic reticulum membrane and the nuclear envelope, and it possesses four transmembrane helices and an EXPERA domain characteristic of the EBP family. Beyond its enzymatic role, EBP is a high-affinity binding protein for emopamil and related sigma-receptor/antiischemic ligands, and it is a component of the microsomal antiestrogen binding site (AEBS), a complex with DHCR7 that carries cholesterol-5,6-epoxide hydrolase (ChEH) activity and is a target of tamoxifen. Loss of isomerase activity causes X-linked dominant chondrodysplasia punctata 2 (CDPX2 / Conradi-Hunermann-Happle syndrome), characterised by accumulation of 8-dehydrocholesterol and 8(9)-cholestenol, chondrodysplasia punctata, ichthyosis, cataracts and short stature; hypomorphic hemizygous variants in males cause MEND syndrome.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: EBP is an ER-resident membrane enzyme; the phylogenetic (IBA) ER localization is correct. ER membrane is the more precise, core location, so this broader ER term is kept as non-core. Reason: ER localization is well supported experimentally, but the endoplasmic reticulum membrane (GO:0005789) captures the precise compartment for this multi-pass membrane enzyme; this broader term is retained but non-core. Supporting Evidence: PMID:8798407 This endoplasmic reticulum-resident membrane protein |
| GO:0006695 cholesterol biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: EBP catalyses a post-lanosterol step of cholesterol biosynthesis; the IBA involvement in cholesterol biosynthetic process is a core biological-process annotation. Reason: The sterol Delta8-Delta7 isomerization catalysed by EBP is an intermediate step in the conversion of lanosterol to cholesterol, well supported across orthologs and by human disease genetics. Supporting Evidence: PMID:10391219 catalyses an intermediate step in the conversion of lanosterol to cholesterol |
| GO:0000247 C-8 sterol isomerase activity | IBA GO_REF:0000033 | ACCEPT | Summary: C-8 sterol isomerase activity is the core molecular function of EBP, moving the Delta(8) double bond to Delta(7). The phylogenetic annotation matches the biochemically demonstrated activity. Reason: EBP is the sterol Delta8-Delta7 (C-8 sterol) isomerase; activity was demonstrated by yeast complementation and mutagenesis and is the enzyme's defining function. Supporting Evidence: PMID:8798407 catalyzes the conversion of delta8-sterols to their corresponding PMID:9894009 exhibits sterol Delta8-Delta7 |
| GO:0004769 steroid Delta-isomerase activity | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Steroid Delta-isomerase activity is the more general parent of the C-8 sterol isomerase activity that EBP performs; the IBA annotation is consistent with the demonstrated function. Reason: This is a broader grouping term for the sterol double-bond isomerase activity; the specific C-8 sterol isomerase activity (GO:0000247) is the core molecular function, so the general term is retained as non-core. Supporting Evidence: PMID:9894009 exhibits sterol Delta8-Delta7 |
| GO:0005635 nuclear envelope | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: EBP is detected on the nuclear envelope in addition to the ER, consistent with the SubCell-vocabulary IEA mapping. Reason: Nuclear-envelope localization is experimentally documented (PMID:10406945) but is secondary to the ER membrane, where the enzyme principally acts. Supporting Evidence: PMID:10406945 associated with the endoplasmic reticulum and with the |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: ER membrane is the core subcellular location of this multi-pass membrane enzyme; the SubCell IEA mapping is correct. Reason: EBP is a multi-pass endoplasmic reticulum membrane protein where sterol isomerization occurs; supported experimentally and by the four predicted transmembrane helices. Supporting Evidence: PMID:8798407 This endoplasmic reticulum-resident membrane protein |
| GO:0016020 membrane | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic membrane localization from the InterPro-to-GO mapping. EBP is indeed an integral membrane protein, but this parent term is uninformative given the specific ER membrane annotation. Reason: The unqualified membrane term is subsumed by the more precise endoplasmic reticulum membrane (GO:0005789) annotation and adds no information. Supporting Evidence: PMID:7706302 Hydrophobicity plots predicted four transmembrane segments |
| GO:0016125 sterol metabolic process | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Sterol metabolic process is a correct but general parent of the cholesterol biosynthetic process in which EBP acts. Reason: Correct high-level process term; the specific role is in cholesterol biosynthesis (GO:0006695), so this broader term is retained as non-core. Supporting Evidence: PMID:8798407 Delta8-delta7 sterol isomerase is an essential enzyme on the sterol biosynthesis |
| GO:0031410 cytoplasmic vesicle | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: EBP redistributes to cytoplasmic vesicles specifically during mitosis when the nuclear membranes break down; a transient, cell-cycle-dependent localization. Reason: Experimentally observed only during mitosis (PMID:10406945); not the resting/core compartment for enzymatic function. Supporting Evidence: PMID:10406945 delocalized during the cell cycle at the mitosis step when the nuclear membranes |
| GO:0033963 cholesterol-5,6-oxide hydrolase activity | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: As a component of the AEBS complex with DHCR7, EBP contributes to cholesterol-5,6-epoxide hydrolase (ChEH) activity, a tamoxifen-inhibited activity distinct from its isomerase function. Reason: ChEH activity is a genuine, experimentally supported activity of the EBP-DHCR7 (AEBS) complex, but is a secondary/complex-level function; the precise contribution of each subunit is not resolved. Retained as non-core rather than as the enzyme's core MF. Supporting Evidence: PMID:20615952 cholesterol-5,6-epoxide hydrolase (ChEH) |
| GO:0047750 cholestenol delta-isomerase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Cholestenol delta-isomerase activity (EC 5.3.3.5, lathosterol <-> 5alpha-cholest-8-en- 3beta-ol) is precisely the EBP-catalysed Delta8-Delta7 isomerase reaction. Reason: This EC 5.3.3.5 term corresponds exactly to EBP's demonstrated sterol Delta8-Delta7 isomerase activity; it is a valid alternative label for the core molecular function. Supporting Evidence: PMID:9894009 isomerase activity (EC 5.3.3.5) upon heterologous expression in a sterol |
| GO:0005515 protein binding | IPI PMID:25910212 Widespread macromolecular interaction perturbations in human... | MARK AS OVER ANNOTATED | Summary: Generic protein binding from a high-throughput interactome-perturbation screen; not informative about EBP's molecular function. Reason: Bare protein binding (GO:0005515) from a large-scale interactome study conveys no specific functional information and is subsumed by the enzyme's characterized activity; marked as over-annotated rather than removed, per experimental-IPI policy. Supporting Evidence: PMID:25910212 Widespread macromolecular interaction perturbations in human genetic disorders |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: Generic protein binding from the HuRI binary interactome map; uninformative as to molecular function. Reason: Bare protein binding (GO:0005515) from a systematic interactome screen adds no functional specificity; marked as over-annotated rather than removed. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome |
| GO:0042802 identical protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | KEEP AS NON CORE | Summary: EBP self-associates as a homodimer; identical protein binding is consistent with the documented EBP-EBP interaction and cross-linking-induced homodimerization. Reason: Homodimerization is corroborated by the UniProt IntAct Q15125-Q15125 self-interaction and by chemical cross-linking data; a real but non-core property of the enzyme. Supporting Evidence: PMID:12760743 Chemical cross-linking induced homodimerization of EBPL and EBP |
| GO:0000247 C-8 sterol isomerase activity | IEA GO_REF:0000107 | ACCEPT | Summary: Electronic ortholog transfer of the core C-8 sterol isomerase activity; consistent with the experimentally demonstrated function. Reason: Duplicate of the core molecular function via Ensembl Compara ortholog transfer; correct. Supporting Evidence: PMID:8798407 catalyzes the conversion of delta8-sterols to their corresponding |
| GO:0006695 cholesterol biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic annotation to cholesterol biosynthetic process; matches the enzyme's role in post-lanosterol cholesterol synthesis. Reason: Consistent with the experimentally and phylogenetically supported role of EBP in cholesterol biosynthesis. Supporting Evidence: PMID:10391219 catalyses an intermediate step in the conversion of lanosterol to cholesterol |
| GO:0006695 cholesterol biosynthetic process | TAS Reactome:R-HSA-6807047 | ACCEPT | Summary: Reactome traceable-author annotation placing EBP in the Bloch (via desmosterol) cholesterol biosynthesis pathway. Reason: EBP isomerizes zymosterol to cholesta-7,24-dien-3beta-ol in the Bloch pathway; a core cholesterol-biosynthesis process annotation. Supporting Evidence: Reactome:R-HSA-6807047 Cholesterol biosynthesis via desmosterol (Bloch pathway) |
| GO:0006695 cholesterol biosynthetic process | TAS Reactome:R-HSA-9969901 | ACCEPT | Summary: Reactome traceable-author annotation placing EBP in the modified Kandutsch-Russell cholesterol biosynthesis pathway (zymostenol to lathosterol). Reason: EBP isomerizes zymostenol to lathosterol in the modified Kandutsch-Russell pathway; a core cholesterol-biosynthesis process annotation. Supporting Evidence: Reactome:R-HSA-9969901 Cholesterol biosynthesis from zymosterol (modified Kandutsch-Russell |
| GO:0004769 steroid Delta-isomerase activity | EXP PMID:10391218 Mutations in a delta 8-delta 7 sterol isomerase in the tatte... | KEEP AS NON CORE | Summary: Experimental identification of EBP (Ebp) as the delta8-delta7 sterol isomerase mutated in the tattered mouse and CDPX2, supporting the (general) steroid Delta-isomerase activity. Reason: The essence (sterol double-bond isomerase) is correct, but the specific C-8 sterol isomerase activity (GO:0000247) captures the function more precisely; this broader term is retained as non-core. Supporting Evidence: PMID:10391218 delta8-delta7 sterol isomerase |
| GO:0004769 steroid Delta-isomerase activity | EXP PMID:10391219 Mutations in the gene encoding 3 beta-hydroxysteroid-delta 8... | KEEP AS NON CORE | Summary: Experimental support for EBP as 3beta-hydroxysteroid-delta8,delta7-isomerase from CDPX2 genetics and yeast functional validation; the general steroid Delta-isomerase grouping is correct. Reason: Correct grouping term; the specific C-8 sterol isomerase activity (GO:0000247) is the core molecular function, so this parent is retained as non-core. Supporting Evidence: PMID:10391219 defects in sterol-delta8-isomerase cause CDPX2 |
| GO:0005783 endoplasmic reticulum | IDA GO_REF:0000052 | KEEP AS NON CORE | Summary: Immunofluorescence-based ER localization of EBP; correct but broader than the ER membrane, where the enzyme resides. Reason: Direct assay supports ER localization; ER membrane (GO:0005789) is the precise core compartment, so this broader term is retained as non-core. Supporting Evidence: PMID:10406945 associated with the endoplasmic reticulum and with the |
| GO:0031965 nuclear membrane | IDA GO_REF:0000052 | KEEP AS NON CORE | Summary: Nuclear-membrane localization from immunofluorescence, consistent with EBP detection on the outer and inner nuclear-envelope membranes. Reason: Experimentally documented but secondary to the ER membrane; retained as non-core. Supporting Evidence: PMID:10406945 associated with the endoplasmic reticulum and with the |
| GO:0031410 cytoplasmic vesicle | EXP PMID:10406945 Colocalization of sterol isomerase and sigma(1) receptor at ... | KEEP AS NON CORE | Summary: EBP redistributes to cytoplasmic vesicles during mitosis, a transient cell-cycle localization directly observed by microscopy. Reason: Observed only during mitosis when nuclear membranes disperse; not the resting core compartment. Supporting Evidence: PMID:10406945 delocalized during the cell cycle at the mitosis step when the nuclear membranes |
| GO:0047750 cholestenol delta-isomerase activity | EXP PMID:12760743 Cloning of an emopamil-binding protein (EBP)-like protein th... | ACCEPT | Summary: Experimental characterization of EBP's EC 5.3.3.5 sterol delta8-delta7 isomerase (cholestenol delta-isomerase) activity via mutagenesis. Reason: This EC 5.3.3.5 term is exactly EBP's demonstrated Delta8-Delta7 isomerase activity; a valid label for the core molecular function. Supporting Evidence: PMID:12760743 3beta-hydroxysteroid sterol delta8-delta7 isomerase activity |
| GO:0047750 cholestenol delta-isomerase activity | EXP PMID:8798407 Emopamil-binding protein, a mammalian protein that binds a s... | ACCEPT | Summary: Functional yeast-complementation evidence that EBP catalyses the delta8-delta7 sterol isomerization (EC 5.3.3.5). Reason: Directly demonstrates the core Delta8-Delta7 isomerase (cholestenol delta-isomerase, EC 5.3.3.5) activity of EBP. Supporting Evidence: PMID:8798407 catalyzes the conversion of delta8-sterols to their corresponding |
| GO:0047750 cholestenol delta-isomerase activity | EXP PMID:9894009 Histidine77, glutamic acid81, glutamic acid123, threonine126... | ACCEPT | Summary: Ala-scanning mutagenesis confirming EBP's sterol Delta8-Delta7 isomerase (EC 5.3.3.5) activity and identifying its catalytic residues. Reason: Direct experimental confirmation of the core EC 5.3.3.5 isomerase activity. Supporting Evidence: PMID:9894009 isomerase activity (EC 5.3.3.5) upon heterologous expression in a sterol |
| GO:0005789 endoplasmic reticulum membrane | IDA PMID:10406945 Colocalization of sterol isomerase and sigma(1) receptor at ... | ACCEPT | Summary: Direct-assay evidence that EBP is active at the endoplasmic reticulum membrane, its core catalytic compartment. Reason: ER membrane is the site of the sterol isomerization reaction; is_active_in is the appropriate qualifier for this multi-pass membrane enzyme. Supporting Evidence: PMID:10406945 associated with the endoplasmic reticulum and with the |
| GO:0033963 cholesterol-5,6-oxide hydrolase activity | IMP PMID:20615952 Identification and pharmacological characterization of chole... | KEEP AS NON CORE | Summary: EBP contributes to cholesterol-5,6-epoxide hydrolase (ChEH) activity as part of the AEBS complex with DHCR7; a tamoxifen-inhibited activity distinct from its isomerase role. Reason: ChEH activity is a genuine, experimentally supported activity of the EBP-DHCR7 (AEBS) complex, but the precise contribution of each subunit is undefined and it is not the enzyme's core molecular function; retained as non-core per experimental-annotation policy. Supporting Evidence: PMID:20615952 composed of 3beta-hydroxysterol-Delta8-Delta7-isomerase (D8D7I) and |
| GO:0004769 steroid Delta-isomerase activity | IDA PMID:10391219 Mutations in the gene encoding 3 beta-hydroxysteroid-delta 8... | KEEP AS NON CORE | Summary: Direct-assay support (yeast expression of patient alleles) for EBP's sterol delta8-isomerase activity, under the general steroid Delta-isomerase grouping. Reason: Correct but general; the specific C-8 sterol isomerase activity (GO:0000247) is the core function, so this parent is retained as non-core. Supporting Evidence: PMID:10391219 defects in sterol-delta8-isomerase cause CDPX2 |
| GO:0004769 steroid Delta-isomerase activity | IMP PMID:10391219 Mutations in the gene encoding 3 beta-hydroxysteroid-delta 8... | KEEP AS NON CORE | Summary: Mutational (patient-allele) evidence for EBP's steroid Delta-isomerase activity from CDPX2 genetics and yeast functional validation. Reason: Correct general grouping term; the specific C-8 sterol isomerase activity (GO:0000247) captures the function precisely, so this parent is retained as non-core. Supporting Evidence: PMID:10391219 defects in sterol-delta8-isomerase cause CDPX2 |
| GO:0005789 endoplasmic reticulum membrane | ISM PMID:7706302 Phenylalkylamine Ca2+ antagonist binding protein. Molecular ... | ACCEPT | Summary: Sequence-model inference of ER membrane localization from the four predicted transmembrane segments and the C-terminal ER-retrieval signal. Reason: Consistent with the experimentally confirmed ER membrane localization; the cloning paper predicted four transmembrane segments and an ER-retrieval motif. Supporting Evidence: PMID:7706302 Hydrophobicity plots predicted four transmembrane segments |
| GO:0008203 cholesterol metabolic process | IMP PMID:10391219 Mutations in the gene encoding 3 beta-hydroxysteroid-delta 8... | KEEP AS NON CORE | Summary: EBP loss-of-function (CDPX2) perturbs cholesterol metabolism, supporting involvement in the cholesterol metabolic process (parent of biosynthesis). Reason: Correct but broader than cholesterol biosynthetic process (GO:0006695), which is the precise role; retained as non-core. Supporting Evidence: PMID:10391219 catalyses an intermediate step in the conversion of lanosterol to cholesterol |
| GO:0043931 ossification involved in bone maturation | IMP PMID:10391219 Mutations in the gene encoding 3 beta-hydroxysteroid-delta 8... | KEEP AS NON CORE | Summary: The skeletal (chondrodysplasia punctata) phenotype of CDPX2 reflects disrupted sterol biosynthesis; the authors infer a role for sterols in bone development. Reason: This is a downstream developmental consequence of the enzyme's metabolic defect, not a direct molecular role of EBP in the ossification machinery; retained as a non-core pleiotropic/developmental annotation. Supporting Evidence: PMID:10391219 defects in sterol-delta8-isomerase cause CDPX2 and suggest a role for sterols in |
| GO:0000247 C-8 sterol isomerase activity | ISS GO_REF:0000024 | ACCEPT | Summary: Sequence-similarity transfer of the core C-8 sterol isomerase activity; consistent with the experimentally demonstrated function. Reason: Duplicate of the core molecular function via curated ortholog similarity; correct. Supporting Evidence: PMID:8798407 catalyzes the conversion of delta8-sterols to their corresponding |
| GO:0004769 steroid Delta-isomerase activity | IDA PMID:9894009 Histidine77, glutamic acid81, glutamic acid123, threonine126... | KEEP AS NON CORE | Summary: Direct-assay support for EBP's sterol Delta8-Delta7 isomerase activity via yeast expression and mutagenesis, under the general steroid Delta-isomerase grouping. Reason: Correct but general; the specific C-8 sterol isomerase activity (GO:0000247) is the core function, so this parent is retained as non-core. Supporting Evidence: PMID:9894009 exhibits sterol Delta8-Delta7 |
| GO:0005635 nuclear envelope | IDA PMID:10406945 Colocalization of sterol isomerase and sigma(1) receptor at ... | KEEP AS NON CORE | Summary: Direct microscopy localizing EBP to the nuclear envelope (outer and inner membranes) in addition to the ER. Reason: Experimentally documented but secondary to the ER membrane; retained as non-core. Supporting Evidence: PMID:10406945 associated with the endoplasmic reticulum and with the |
| GO:0005783 endoplasmic reticulum | IDA PMID:10406945 Colocalization of sterol isomerase and sigma(1) receptor at ... | KEEP AS NON CORE | Summary: Direct microscopy localizing EBP to the endoplasmic reticulum; correct but broader than the ER membrane where the enzyme acts. Reason: Direct assay supports ER localization; ER membrane (GO:0005789) is the precise core compartment, so this broader term is retained as non-core. Supporting Evidence: PMID:10406945 associated with the endoplasmic reticulum and with the |
| GO:0006695 cholesterol biosynthetic process | IDA PMID:9894009 Histidine77, glutamic acid81, glutamic acid123, threonine126... | ACCEPT | Summary: Direct-assay evidence tying EBP's isomerase activity to cholesterol biosynthesis (yeast Delta5,7-sterol production); a core process annotation. Reason: EBP catalyses an obligatory post-lanosterol isomerization step of cholesterol biosynthesis; directly supported. Supporting Evidence: PMID:8798407 Delta8-delta7 sterol isomerase is an essential enzyme on the sterol biosynthesis |
| GO:0005789 endoplasmic reticulum membrane | TAS Reactome:R-HSA-195690 | ACCEPT | Summary: Reactome traceable-author annotation locating the EBP-catalysed zymosterol isomerization at the ER membrane. Reason: Consistent with the experimentally confirmed ER membrane localization and site of catalysis. Supporting Evidence: Reactome:R-HSA-195690 Zymosterol is isomerized to cholesta-7,24-dien-3beta-ol |
| GO:0005789 endoplasmic reticulum membrane | TAS Reactome:R-HSA-6807052 | ACCEPT | Summary: Reactome traceable-author annotation locating the EBP-catalysed zymostenol-to-lathosterol isomerization at the ER membrane. Reason: Consistent with experimentally confirmed ER membrane localization and site of catalysis. Supporting Evidence: Reactome:R-HSA-6807052 EBP isomerizes ZYMSTNL to LTHSOL |
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Download this section (compressed HTML)Q: Within the AEBS (EBP-DHCR7) complex, does EBP itself contribute the catalytic cholesterol-5,6-epoxide hydrolase activity, or is it a scaffolding/regulatory partner of DHCR7?
Experiment: Reconstitute purified EBP and DHCR7 separately and together in defined liposomes and assay ChEH activity to resolve which subunit carries the epoxide-hydrolase catalysis.
Experiment: Use the available cryo-EM/X-ray structures (PDB 6OHT, 8W0R) to model catalytic-residue (H77, E81, E123, T126, N194, W197) positioning relative to bound sterol and validate by structure-guided mutagenesis of the Delta8-Delta7 isomerization.
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